Touch systems are well known in the art and typically include a touch screen having a touch surface on which contacts are made using a pointer in order to generate user input. Pointer contacts with the touch surface are detected and are used to generate corresponding output depending on areas of the touch surface where the pointer contacts are made. Common touch systems utilize analog resistive, electromagnetic, capacitive, acoustic or machine vision techniques to identify pointer contacts on the touch surface.
For example, International PCT Application No. PCT/CA01/00980 filed on Jul. 5, 2001 and published under No. WO 02/03316 on Jan. 10, 2002, assigned to SMART Technologies Inc., assignee of the present invention, discloses a camera-based touch system comprising a touch screen that includes a passive touch surface on which a computer-generated image is presented. A rectangular bezel or frame surrounds the touch surface and supports digital cameras at its corners. The digital cameras have overlapping fields of view that encompass and look generally across the plane of the touch surface. The digital cameras acquire images looking across the touch surface from different locations and generate image data. Image data acquired by the digital cameras is processed by digital signal processors to determine if a pointer exists in the captured image data. When it is determined that a pointer exists in the captured image data, the digital signal processors convey pointer characteristic data to a master controller, which in turn processes the pointer characteristic data to determine the location of the pointer in (x,y)-co-ordinates relative to the touch surface using triangulation. The pointer co-ordinate data is conveyed to a computer executing one or more applications programs. The computer uses the pointer co-ordinate data to update the computer-generated image that is presented on the touch surface. Pointer contacts on the touch surface can therefore be recorded as writing or drawing or used to control execution of applications programs executed by the computer.
Although the above touch system works extremely well, improvements in vision-based touch systems are continually being sought.
It is therefore an object of the present invention to provide a novel apparatus and method for detecting a pointer relative to a touch surface.